【摘要】 北西走向的孝丰—三门湾断裂是浙北地区一条重要的断裂。该断裂第四纪以来表现为左旋走滑,并水平断错了北东走向的萧山—球川断裂和东西走向的昌化—普陀断裂。这三条断裂交汇于杭州地区并造成了钱塘江的拐弯。在孝丰—三门湾断裂与北东走向断裂的交汇处曾有多次地震发生。通过在孝丰—三门湾断裂(杭州段)上布设的4个探槽,发现该断裂附近存在一系列近于东西走向及北东走向的晚更新世活动断裂。这些断层活动可能是由孝丰—三门湾主干断裂的活动引起的,并调节着孝丰—三门湾主干断裂的活动,减弱断裂附近应力,降低区域地震危害性。采用了光释光(OSL)测年方法来限定断层活动时代,并采用孢粉测年对OSL年龄进行验证。依据OSL年龄,探槽所揭露的断层活动均发生距今1.65万年之前,存在两次断层活动,分别发生于1.65~1.97万年和4.2~5.12万年。孝丰—三门湾断裂在晚更新世有所活动的认识对于杭州地区乃至整个浙北地区未来的地震危险性评价具有重要的意义。更多还原

【Abstract】 The NW-SE trending Xiaofeng-Sanmen fault(XSF)is a major fault in Hangzhou region.The XSF is of left-lateral strike-slip character since late Quaternary and dislocated the NE trending Xiaoshan-Qiuchuan fault(XQF)and the EW trending Changhua-Putuo fault(CPF).These three faults meet together in Hangzhou region and make the Qiantang River turn around. Along the XSF,there are several earthquakes(M≤5)took place at the intersection area with the NE trending fault.Because of strong weathering,the geomorphological traces related to faults are hardly to be found and measured.Based on the observation of outcrops and geophysical exploration,four trenches were excavated on XSF in Hangzhou Region.These trenches exposed that the EW and NE trending faults were active along the XSF.These fault movements might be triggered by the activities of XSF which made the pre-existing fracture active in the Late Quaternary.The fault movements reduced the stress along the XSF and depressedthe seismic risk for the Hangzhou region.Optically stimulated luminesence(OSL)samples of sediments were collected trying to get timing of the fault movements.The OSL ages are validated by sporopollen analysis.According to the OSL ages,the timing of fault movements could be grouped into two periods:(16.5~19.7)ka BP and(42.0~51.2)ka BP.The fault activities of XSF during the Late Quaternary are very important for regional seismic risk assessment.更多还原